Telephone ringing control circuits

Abstract

A single channel carrier system for telephone service is disclosed including a remote terminal having a ringing generator included therein for generating ringing signals to operate the ringers of remote subscribers. The ringing generator is a dc-to-dc converter for stepping up a battery voltage to ringing voltage level that is interrupted at a 20 Hz rate. The generation of ringing signals is controlled by a carrier signal interrupted at a ringing rate. Detection of the ringing signals on the carrier utilizes a delay circuit to prevent response to inadvertent signals as well as delay hysteresis to ensure the bridging of detection from one 20 Hz cycle to the next. The ringing generator must also be regulated, both in current and in voltage, to prevent danger to personnel, damage to equipment, and excessive power consumption.

What is claimed is: 
     
       1. A delay circuit having a hysteresis delay characteristic comprising an integrating detector,   a threshold responsive means connected to said detector and including threshold establishing means, and   feedback means from said threshold responsive means for altering said threshold establishing means.   
     
     
       2. The delay circuit according to claim 1 wherein said detector comprises a capacitor charged from a voltage source through a transistor switch. 
     
     
       3. The delay circuit according to claim 1 wherein said threshold responsive means comprises a threshold transistor switch connected to a constant voltage biasing device. 
     
     
       4. The delay circuit according to claim 3 wherein said feedback means comprises a transistor switch connected across said constant voltage biasing device. 
     
     
       5. A detection circuit with hangover comprising a source of signals to be detected,   an integrating detector responsive to said signals,   a threshold responsive enabling circuit connected to said integrating detector, and   feedback means responsive to said enabling circuit for altering the threshold value of said enabling circuit.   
     
     
       6. A carrier-controlled ringing signal generator comprising a carrier detection circuit,   a ringing signal source,   a variable delay circuit connected between said detection circuit and said ringing signal source for introducing a different delay before the enablement of said source than before the disablement of said source,   said delay comprising   a timing circuit responsive to said detection circuit for generating a timing signal,   threshold responsive means responsive to said timing signal for enabling said source, and   means responsive to the enablement of said source for changing the threshold value of said threshold responsive means.   
     
     
       7. A ringing signal envelope detector comprising; a charging circuit responsive to ringing signals for enabling a charging current path,   a capacitor in said charging circuit,   a threshold detection circuit connected across said capacitor, and   means responsive to a signal exceeding said threshold for reducing said threshold by a preselected amount.   
     
     
       8. The envelope detector according to claim 7 wherein said threshold detector includes a first transistor,   a semiconductor junction threshold device connected to the emitter of said transistor, and   a second transistor having its collectoremitter path connected in parallel with said device.